1. Technical Field of the Invention
The present invention relates to a device for converting a constant speed rotational drive to a linear reciprocating motion, in particular to a linear reciprocating motion device which can perform a linear reciprocating motion of arbitrary speed pattern and an optical card transporting and holding device which employs the same reciprocating motion device.
2. Prior Art
In general, in a field such as the machine tool field, it becomes frequently necessary to give a linear reciprocating motion to a material to be scraped or cut. Such a linear reciprocating motion is also employed in the fields of precision machinery, office automation apparatus, printing devices, and so forth, in addition to the machine tool field.
Moreover, in carrying out recording and reproducing for an optical recording medium of the card type (referred to as the optical card hereinafter) which is being watched lately, it is also necessary to move the optical card in a reciprocating manner along a straight line.
In recording information on the optical card, information is recorded on the reflecting surface side of the optical card as a group of fine holes that are disposed linearly parallel to the edge of the optical card. In order to record information in this manner, or to read information that is recorded in such a fashion, laser light from the pickup unit of the optical system that is focused on the reflecting surface of the optical card has to be moved relative to the row of information holes. That is, by giving the optical card a linear reciprocating motion, laser light is arranged to trace the row of information holes.
Further, in addition to the linear reciprocating motion of the optical card, in order to be able to read information from any location on the optical card, the optical pickup unit that reads information by the use of the reflected laser light has to be moved linearly in the direction which is perpendicular to the direction of the linear reciprocating motion of the optical card, as well as in the direction parallel to the optical card, as shown in FIG. 1.
As a device for giving the optical card a linear reciprocating motion, there is known a method in which the repeated forward and backward motion of a motor is converted into a linear reciprocating motion by means of belts or racks and pinions or like devices. However, in the method where the forward and reverse rotation of the motor are repeated for each round trip of the linear motion, it is necessary to repeat to build up the motor to a high speed, decelerate it quickly, and build up again the reverse rotation of the motor, in a short time. Moreover, the power of the motor has to be sufficiently high in order for these operations to be accomplished with ease.
Further, by rotating the motor continuiously in one direction, instead of switching between forward rotation and reverse rotation, and by the use of a crank mechanism as shown in FIG. 2, there may also be obtained a linear reciprocating motion. Let R represent the length of the crank arm L, the length of the linking rod S, and the stroke of the linear reciprocating motion of the optical card. When the crank arm rotates due to the rotation of the motor with a fixed angular velocity .omega., the motion will be described by ##EQU1## One notes, however, that this motion does not satisfy the condition of a motion with constant speed. It is said that the linear reciprocating motion for the optical card during recording and reproducing requires a linear reciprocating motion with constant speed of sufficient precision.
To obtain a constant linear reciprocating motion by the use of a crank mechanism, there may be considered the following electrical rotation speed control method. Namely, by detecting the moving speed and the angular phase of the crank mechanism, and feeding these data back to the rotation driving unit of the motor, the rotation speed of the motor is varied by comparing the value fed back and the speed of motor rotation. In connection with this method, however, there arises not only the problem of intricacy of the control circuit but also such problems as the inertia on the motor and the increased burden on the electrical control of acceleration and deceleration.
Moreover, in order to carry out recording or reproducing for card 1 with such a transporting and holding device, the optical card 1 has to be given a reciprocating motion that has a speed which is practical for recording and reproducing (for instance, about 3.5 Hz), so that care has to be taken to prevent slippage in positioning of the optical card 1 during recording and reproducing. Moreover, it is desirable for the operator that the operation of insertion and retrieval of the optical card 1 is easy to perform.